The present invention relates to proximity switches, and, more particularly, to a generally cylindrical, magnetic proximity switch that provides for an extended sensing range and includes visual indicators spaced at intervals about the body of the switch to provide immediate visual indication as to the status of the switch.
Magnetic proximity switches are commonly used for linear position sensing. A typical magnetic proximity switch includes a switching circuit that is housed within an elongated, generally cylindrical body near a distal end of the cylindrical body. This switching circuit is closed when a target object passes within a predetermined range from the distal end of the cylindrical body. To facilitate installation, the cylindrical body of such prior art proximity switches commonly have a threaded shank portion. The switch thus can be threaded in and through a bore with corresponding threads for simple installation.
The physical structure of the switching circuit in prior art switches may vary. For example, Applicant manufactures one such proximity switch wherein a primary magnet is housed within the cylindrical body of the switch. This primary magnet is positioned near the end of the switch and is linked by a connecting rod to a bias magnet. The bias magnet controls the movement of a common contact between open and closed positions. A central magnet positioned between the primary and bias magnets attracts the primary magnet and repels the bias magnet, maintaining the primary magnet in a retracted position. However, when a ferrous or magnetic object passes within the sensing area at the end of the switch, the attraction between the primary magnet and central magnet is overcome, and the primary magnet is attracted to the object and moves toward the end of the switch. Thus, the connecting rod pulls the biasing magnet forward, and the bias magnet moves the common contact from a closed position to an open position.
Again, a variety of other magnet configurations may also be used in the switching circuit, but a common problem with prior art proximity switches is their limited sensing range. Often, prior art switches are capable only of sensing ferrous or magnetic objects that pass within 0.100 inches of the end of the switch body. In many applications, the small gap required for the sensing operation precludes the use of prior art switches. For example, debris may accumulate within the gap near the end of the switch, or vibrations or other movement may necessitate greater clearances.
When proximity switches are used for linear position sensing, they are often equipped with a visual indicator, commonly a light-emitting diode (LED), which is energized when the switch moves from one position to another, i.e., from open to closed. However, because these switches are commonly threaded for installation, depending on the rotational orientation of the switch body, the indicator (LED) may or may not be visible. Moreover, typical LEDs may be dim and difficult to see from a distance.
It is thus an object of the present invention to provide a generally cylindrical, magnetic proximity switch that provides for an extended sensing range compared to prior art switches.
It is a further object of the present invention to provide a proximity switch having visual indicators than can be easily seen irrespective of the switch's rotational orientation.
These and other objects and advantages of the present invention will become readily apparent upon a reading of the description herein along with the appended drawings.